State Function
A property whose value depends only on the current state of the system, not on how that state was reached.
Formula / equation
ΔX = X_final − X_initial
Unit
Various
In depth
State functions can be added and subtracted around any cycle to give zero, which is precisely what makes Hess's law and thermodynamic cycles possible. Their changes are written with the delta symbol and require only the initial and final conditions to evaluate.
Examples in the real world
Internal energy, enthalpy, entropy, Gibbs energy, pressure, volume and temperature.